In the practice of audio technology there is often a need to determine the polarity of the phase relationship, i.e. whether "in phase" or "out of phase", between the input and output ports of a functional audio block such as an amplifier or an audio channel which may include several links of different media such as electrical, acoustic, modulated r.f., optical, magnetic, etc., connected in tandem.
A common requirement is to determine or verify polarity at the terminals of transducers such as loudspeakers and microphones.
Another common requirement is to determine the overall phase polarity of an audio channel including an amplifier and a loudspeaker.
Where several loudspeakers are operated together there is a need to ensure that all of the loudspeakers are operating in phase with each other to avoid cancellation and loss of acoustic efficiency and quality. This need for relative phasing applies to both monophonic and stereophonic systems, and applies generally wherever interaction may occur, for example between loudspeakers and microphones.
In professional sound activities, good practice requires at least a general observance of relative phasing to minimize the variables; however as increasingly higher levels of excellence are sought, heightened polarity awareness leads to observance of absolute phase polarity throughout an entire system as verified by polarity testing of all system components, electrical and acoustic.